1. Field of the Invention
The present invention relates to an image formation apparatus utilizing a heat developable transfer type photosensitive member to form images in a copying machine, printer, or the like. More particularly, it relates to control of the image formation process from heat development through pressure transfer.
2. Related Technical Art
Various kinds of methods and apparatus for forming images are known. A conventional image formation apparatus utilizing a heat developable transfer type photosensitive member is disclosed in, for example, Japanese Laid-Open patent No. 62-147461. According to that publication, main elements of the mechanism, such as exposure, heat development, and pressure transfer sections, are each arranged within a single structure for the apparatus. Image formation is then performed according to the following procedure.
A roll-type heat developable transfer-type photosensitive member is first cut into predetermined lengths before being exposed to an image in order to form a latent image. The heat development section next develops the latent image using heat rollers. Then, image-receiving paper is superposed with the photosensitive member, and is transferred by rollers under pressure. The photosensitive member is discharged by a separation device to a photosensitive member disposal section, while the image-receiving paper is discharged to a tray through a fixing device.
Such a prior art color copying machine, uses a photosensitive member with microcapsules including photosensitive materials, polymer compounds, and color materials, coated onto a supporting member, and a transfer member to receive color materials which are transferred from the photosensitive member under pressure. Development is performed in the heat developing section so that the entire contents of the microcapsule, including color materials, are transferred from the photosensitive member to the image receiving paper by the pressure transfer section, thereby copying images.
The above prior art has excellent characteristics in that it is possible to obtain a low-cost and small-sized image forming device, and produce high quality images. However, the prior art also has poor characteristics in that the environmental temperature and humidity of the photosensitive member moving from the heat developing section to the pressure transfer section, may be easily varied by the temperature of the image forming apparatus, which in turn may vary the hardness of the microcapsules, resulting in deterioration of image quality, that is, the image density becomes unstable. In particular, when the environmental temperature is high, the density decreases, and when the environmental temperature is low, the density increases.
Furthermore, other conditions are observed, for example, such as that density gradually decreases in response to increased elapsed time after powering-on. In addition, when an image is continuously output, the density of the output image varies and stable image quality cannot be obtained, and image quality may be further deteriorated, that is, the lowest density increases, or the highest density decreases.
In addition to the above, as another factor, the following situation was observed. Namely, that dispersion in densities increases according to a difference in the devices. The present invention seeks to eliminate the above problems, and its object is to provide an image formation apparatus wherein high quality images are output, that is, the rendering density is uniform and image quality is stable.